Field of the Invention
The invention relates to directional couplers and high speed samplers.
Copending patent application Ser. No. 08/359,090 filed Dec. 19, 1994 describes an electronic material level sensor or "electronic dipstick" based on time domain reflectometry (TDR) of very short electrical pulses. Pulses are propagated along a transmission line or guide wire that is partially immersed in the material being measured. A launcher plate is positioned at the beginning of the guide wire. Reflected pulses are produced at the material interface due to the change in dielectric constant. The time difference of the reflections at the start of the guide wire and at the material interface are used to determine the material level.
However, there is a problem when the reflected pulse returns while the outbound pulse is still being transmitted, i.e. when the reflecting discontinuity is very close to the input or launch end of the transmission line. In these cases it may be necessary to connect the electronics to the transmission line through a cable to sufficiently separate the transmitted and reflected pulses. However, there is a need for a system which does not require a cable wherein the electronics can be connected directly to the launch point of the dipstick.
U.S. Pat. No. 5,345,471 and copending CIP application Ser. No. 08/301,924 filed Sep. 6, 1994 describe an ultra-wideband (UWB) receiver which utilizes a strobed input line with a sampler connected to an amplifier. The outputs of two integrating single-ended samplers are input into a differencing amplifier. The samplers integrate, or average, up to 10,000 pulses.